Question 590911


Looking at the expression {{{5s^2-22s+8}}}, we can see that the first coefficient is {{{5}}}, the second coefficient is {{{-22}}}, and the last term is {{{8}}}.



Now multiply the first coefficient {{{5}}} by the last term {{{8}}} to get {{{(5)(8)=40}}}.



Now the question is: what two whole numbers multiply to {{{40}}} (the previous product) <font size=4><b>and</b></font> add to the second coefficient {{{-22}}}?



To find these two numbers, we need to list <font size=4><b>all</b></font> of the factors of {{{40}}} (the previous product).



Factors of {{{40}}}:

1,2,4,5,8,10,20,40

-1,-2,-4,-5,-8,-10,-20,-40



Note: list the negative of each factor. This will allow us to find all possible combinations.



These factors pair up and multiply to {{{40}}}.

1*40 = 40
2*20 = 40
4*10 = 40
5*8 = 40
(-1)*(-40) = 40
(-2)*(-20) = 40
(-4)*(-10) = 40
(-5)*(-8) = 40


Now let's add up each pair of factors to see if one pair adds to the middle coefficient {{{-22}}}:



<table border="1"><th>First Number</th><th>Second Number</th><th>Sum</th><tr><td  align="center"><font color=black>1</font></td><td  align="center"><font color=black>40</font></td><td  align="center"><font color=black>1+40=41</font></td></tr><tr><td  align="center"><font color=black>2</font></td><td  align="center"><font color=black>20</font></td><td  align="center"><font color=black>2+20=22</font></td></tr><tr><td  align="center"><font color=black>4</font></td><td  align="center"><font color=black>10</font></td><td  align="center"><font color=black>4+10=14</font></td></tr><tr><td  align="center"><font color=black>5</font></td><td  align="center"><font color=black>8</font></td><td  align="center"><font color=black>5+8=13</font></td></tr><tr><td  align="center"><font color=black>-1</font></td><td  align="center"><font color=black>-40</font></td><td  align="center"><font color=black>-1+(-40)=-41</font></td></tr><tr><td  align="center"><font color=red>-2</font></td><td  align="center"><font color=red>-20</font></td><td  align="center"><font color=red>-2+(-20)=-22</font></td></tr><tr><td  align="center"><font color=black>-4</font></td><td  align="center"><font color=black>-10</font></td><td  align="center"><font color=black>-4+(-10)=-14</font></td></tr><tr><td  align="center"><font color=black>-5</font></td><td  align="center"><font color=black>-8</font></td><td  align="center"><font color=black>-5+(-8)=-13</font></td></tr></table>



From the table, we can see that the two numbers {{{-2}}} and {{{-20}}} add to {{{-22}}} (the middle coefficient).



So the two numbers {{{-2}}} and {{{-20}}} both multiply to {{{40}}} <font size=4><b>and</b></font> add to {{{-22}}}



Now replace the middle term {{{-22s}}} with {{{-2s-20s}}}. Remember, {{{-2}}} and {{{-20}}} add to {{{-22}}}. So this shows us that {{{-2s-20s=-22s}}}.



{{{5s^2+highlight(-2s-20s)+8}}} Replace the second term {{{-22s}}} with {{{-2s-20s}}}.



{{{(5s^2-2s)+(-20s+8)}}} Group the terms into two pairs.



{{{s(5s-2)+(-20s+8)}}} Factor out the GCF {{{s}}} from the first group.



{{{s(5s-2)-4(5s-2)}}} Factor out {{{4}}} from the second group. The goal of this step is to make the terms in the second parenthesis equal to the terms in the first parenthesis.



{{{(s-4)(5s-2)}}} Combine like terms. Or factor out the common term {{{5s-2}}}



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Answer:



So {{{5s^2-22s+8}}} factors to {{{(s-4)(5s-2)}}}.



In other words, {{{5s^2-22s+8=(s-4)(5s-2)}}}.



Note: you can check the answer by expanding {{{(s-4)(5s-2)}}} to get {{{5s^2-22s+8}}} or by graphing the original expression and the answer (the two graphs should be identical).


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